An MIMO (Multiple Input Multiple Output, multiple input multiple output) system that performs precoding based on a codebook is a manner used by mainstream wireless cellular systems under FDD (Frequency Division Duplex, frequency division duplex) standards. The so-called precoding based on a codebook refers to that a receiving end measures a wireless channel from a transmitting end to itself, selects one matrix (hereinafter referred to as a codebook element) from a predefined set of matrices (hereinafter the set of matrices is referred to as a codebook) known to the transmitting end and the receiving end, and feeds back an index value (Precoding Matrix Indicator, PMI) corresponding to the matrix to the transmitting end, so that the transmitting end learns a channel from itself to the receiving end, and further may select to apply the precoding matrix to signals to be transmitted (such a processing procedure is called precoding), and then transmit the signals. It is assumed that a base station is used as the transmitting end, and a terminal is used as the receiving end. In an LTE (Long Time Evolution, long term evolution) system, the base station is referred to as an eNodeB (Evolved NodeB, evolved base station), and the terminal is referred to as a UE (User Equipment, user equipment). Generally, the eNodeB and the UE store one or more codebooks at the same time, and if a plurality of codebooks is stored, generally different codebooks correspond to different quantities of transmit antennas. After being powered on, the eNodeB broadcasts public information of a cell, for example, the number of transmit antennas configured by the eNodeB, to UEs within its coverage. In addition, the eNodeB informs each UE of a transmission mode being currently used, and then the UE derives according to the information whether the eNodeB transmits signals in a precoding manner, and derives which codebook is used for precoding. The UE measures a channel from the eNodeB to itself, selects an optimal codebook element from the codebook according to preset criteria or methods, and then feeds back PMI corresponding to the codebook element to the eNodeB. After receiving the PMI fed back by the UE, the eNodeB can learn precoding information of the channel from the eNodeB to the UE, and then starts a scheduling process by using the information (and other information).
In LTE Release (release) 8 to Release 10, codebooks are designed for 2, 4 and 8 antennas corresponding to different antenna configuration based on certain criteria. Criteria for designing a 2-antenna codebook are based on DFT (Discrete Fourier Transform, discrete Fourier transform), with 4 codebook elements at most. Criteria for designing a 4-antenna codebook are based on Householder transformation, with 16 codebook elements at most. Criteria for designing an 8-antenna codebook are based on a dual codebook structure, with 256 codebook elements at most.
Because the design of the existing codebooks is set based on single-user MIMO, the accuracy is low, and even becomes lower when the codebook is applied to multi-user MIMO.